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Using 'Unique Solution' to help solve http://www.calcudoku.org/forum/viewtopic.php?f=3&t=439 
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Author:  mparisi [ Mon May 13, 2013 12:07 am ] 
Post subject:  Re: Using 'Unique Solution' to help solve 
mce wrote: And it's even impossible not to use this if one ends up spotting that a certain combination of numbers cannot be right as otherwise the solution would not be unique. It's not something one can "unlearn on demand". Huh? Just because you see that you could eliminate some combination of numbers because then the solution wouldn't be unique doesn't mean that you have to use that information in trying to find your solution. In fact if you start with the premise that the solution might not be unique you will ignore this sort of thing. 
Author:  tommyp0123 [ Tue May 14, 2013 5:33 am ] 
Post subject:  Re: Using 'Unique Solution' to help solve 
mce wrote: tommyp0123 wrote: picklepep wrote: I disagree. The unique solution is a criteria and a stricture to these puzzles. It is a given much like that of there only being one iteration of a number in a row or column. I don't believe in selfimposed limits when we are solving these puzzles. To do so would limit my ability to sharpen my skill, or gain insight in the way the numbers work together. I can think of a few puzzles where if I hadn't used this method the only alternative would have been the old 'trial and error'. Now if I had an alternative between using two methods, one of which was plugging in numbers, and the other which required me to think, I'm going to use the one that sharpens my acumen. I respect that. It's been my experience that I have always found a way to proceed using technique and not bruteforce. I would not call "making use of the uniqueness of the solution" brute force. It's just a piece of info one has from the start. And it's even impossible not to use this if one ends up spotting that a certain combination of numbers cannot be right as otherwise the solution would not be unique. It's not something one can "unlearn on demand". I interpreted trial and error to mean bruteforce, i.e. plugging in numbers. It's true you can't 'unlearn' but you can prove for squares (isn't that what solving is  proving that a certain square must be a certain number) without using that information. It may point you in a particular direction though. 
Author:  nicow [ Wed May 15, 2013 9:37 am ] 
Post subject:  Re: Using 'Unique Solution' to help solve 
In my opinion an unique solution is a matter of trust. My system does some simple logic and then uses trial and error / backtracking. The first solution found always happens to be the good one. As this is not satisfying, I made a simple module that evaluates all candidates. Nogood candidates are sorted out. If then a solution is found, it is certainly the only one. Btw, for the more difficult puzzles, this module reduces the time needed for trial and error. 
Author:  mce [ Sat May 18, 2013 1:47 pm ] 
Post subject:  Re: Using 'Unique Solution' to help solve 
mparisi wrote: mce wrote: And it's even impossible not to use this if one ends up spotting that a certain combination of numbers cannot be right as otherwise the solution would not be unique. It's not something one can "unlearn on demand". Huh? Just because you see that you could eliminate some combination of numbers because then the solution wouldn't be unique doesn't mean that you have to use that information in trying to find your solution. In fact if you start with the premise that the solution might not be unique you will ignore this sort of thing. Of course one does not "absolutely have to use the info", as there is plenty of structure in these puzzles and there always is another way to conclude. But as I wrote, you cannot "unlearn" it either and I see no fun in spending a lot of time in finding an alternative explanation for what I already know. I prefer to discover things that I do not yet know. For those who disagree, here's a new challenge: take a 12x12 and describe every possible path to the solution according to any set of rules you like. Just don't forget to eat, sleep, and live in between. I also don't see what's wrong with using it anyway. After all, we all also use the fact that any number can only occur once in a row/column. It's a given. So is the uniqueness. 
Author:  pnm [ Sat May 18, 2013 2:30 pm ] 
Post subject:  Re: Using 'Unique Solution' to help solve 
And very related, the "noop" puzzles: viewtopic.php?f=16&t=440 E.g. the cage with "2" and 2 cells has to be 2: 2+ obviously doesn't work, and 2x and 2: don't work because the solution is unique (also wrt. the operators (!)) 
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